1. Field of the Invention
The present invention relates to a printing apparatus for printing images and a method of controlling the printing apparatus.
2. Description of the Related Arts
In recent years, printing apparatuses configured to capture image data picked up by an image pickup apparatus, such as a digital camera, and print the image data on a recording medium, such as a print sheet, have come into widespread use in general households.
Conventionally, such printing apparatuses for home use generally use cut sheets for printing. However, print sheets to be contained in a cartridge are not necessarily limited to cut sheets, but roll paper formed by winding belt-like print paper around a roller may be used.
The use of roll paper for printing is advantageous e.g. in that it is possible not only to hold a large amount of print paper in a space-saving cartridge, but also to share a conveying mechanism including a cartridge for different print sizes.
In a case where a cut sheet is used for printing, the cut sheet is required to have a larger size than a print area so as to be held during a printing operation. For this reason, a user sometimes has to cut off a portion of the cut sheet surrounding the print area, which serves to hold the print area, for him/herself after completion of the printing.
On the other hand, in a case where roll paper is used for printing, a cutter for cutting print paper is provided in a printing apparatus, and therefore the printing apparatus is capable of cutting off only a print area to provide the same to the user.
FIG. 10 is a view of a conventional printing apparatus using roll paper in a state immediately before the start of a printing operation. FIG. 11 is a view of the printing apparatus in a state immediately after the end of the printing operation. FIG. 12 is a view of the printing apparatus in a state immediately after the end of a discharge operation.
The sequential printing operations carried out by the conventional printing apparatus will be described with reference to FIGS. 10 to 12.
Roll paper 1 loaded in the printing apparatus is fed by a feed roller, not shown, with its leading end directed forward, to be nipped by a conveying roller pair 4. Thereafter, the roll paper 1 is reciprocated to and fro by the conveying roller pair 4, whereby the sequential operations from printing to discharge are carried out without ever releasing the roll paper 1 from the nipped state.
In the case of printing an image with a length X in a roll paper conveying direction, the roll paper 1 is conveyed by the conveying roller pair 4 until a printing start point S on the roll paper 1, which is located at a distance X from the roll paper leading edge, is brought to a position (print start position) immediately below a heating element of a thermal head 3 (see FIG. 10).
Then, the roll paper 1 is brought into pressure contact with the thermal head 3 and a platen roller 6 opposed to the thermal head 3 at the printing start point S, together with an ink ribbon 2.
Thereafter, the roll paper 1 is conveyed in a direction in which the roll paper leading end moves toward the thermal head 3 (i.e. in a leftward direction as viewed in FIG. 10). Simultaneously, the ink ribbon 2 is conveyed by a ribbon drive mechanism, not shown, in the same direction as the roll paper conveying direction.
At this time, the heating element of the thermal head 3 generates heat, whereby ink on the ink ribbon 2 is transferred onto the roll paper 1 for printing.
The roll paper conveyance is continued until the roll paper leading edge is brought to a position (printing end position) immediately below the heating element of the thermal head 3 (see FIG. 11), whereby the image having the length X (see FIG. 10) is formed.
The ink ribbon 2 is coated with inks of a plurality of colors, such as yellow, magenta, and cyan. Image formation (printing) is performed by transferring the color inks onto the roll paper 1 in superimposed relation. For this reason, the roll paper 1 conveyed to the printing end position is returned again to the print start position by the conveying roller pair 4, and then printing in a next color is repeatedly carried out.
When printing in a final color is completed, the roll paper 1 is conveyed until the printing start point S is moved to a position immediately below a cutter unit 5. Thereafter, the roll paper 1 is cut at the point S by the cutter unit 5, and then only a portion (printout 1-A) having the image formed thereon is discharged (see FIG. 12).
In the case of printing a next image immediately after the above operation, the roll paper 1 is conveyed until a point S′ located at a distance corresponding to a length X′ of the next image which is measured from the point S at which the roll paper 1 is cut is moved to the position immediately below the heating element of the thermal head 3, whereafter the sequential operations described above are carried out again from the start.
When printing is repeatedly carried out in the above-mentioned printing apparatus, heat generated by the heating element of the thermal head 3 is accumulated in the printing apparatus, which causes a progressive rise in the temperature of a component part of the printing apparatus and the ambient temperature within the apparatus. Then, when the temperature of the component part has exceeded a predetermined value, the heat can break the component part or adversely affect the printing process, thereby hindering normal printing operation.
To cope with this problem, a thermistor or the like is provided in the printing apparatus, and when a temperature detected by the thermistor or the like during a printing operation exceeds the predetermined value, the printing operation is temporarily stopped so as to provide heat dissipation time for making the temperature lower than the predetermined value.
In general, a printing operation is stopped in a state where the roll paper 1 is at the print start position (i.e. a state where the printing start point S is positioned immediately below the heating element of the thermal head 3) (see FIG. 10), so that next conveyance for printing can be started immediately after the temperature becomes lower than the predetermined value.
However, when the operation is suspended over a predetermined time period with the roll paper 1 held at the print start position, a portion of the roll paper 1 nipped by the conveying roller pair 4 is recessed.
This recess is created within a print range X′ (S to S′) of a next print image to be printed, and hence when the next image is printed, ink cannot be properly transferred, which hinders excellent printing.
To avoid this problem, there is proposed a method in which a margin is produced on roll paper between an area for printing a first image and an area for printing a second image, so that the marginal portion can be nipped by the conveying roller pair when it is required to stop a printing operation (see e.g. Japanese Paten Laid-Open Publication No. 2003-54054).
In the technique disclosed in Japanese Paten Laid-Open Publication (Kokai) No. 2003-54054, however, since the marginal portion cannot be used as a print area, it is impossible to make fully efficient use of the roll paper 1 without waste.
Further, a complicated mechanism is required for feeding roll paper including the marginal portion and then conveying the roll paper to a printing position again.